This invention relates in general to shaped charge perforators and more particularly, to a shaped charge perforating unit having two high explosive materials.
Explosive shaped charge well perforating devices are often used in perforating well casing and the surrounding earth formations in the production of hydrocarbons. In a typical embodiment, a plurality of shaped charges are mounted in a fluid-tight, cylindrical, metal housing or on an elongated bar member which is adapted to traverse the borehole to be perforated. The shaped charges are mounted in the housing or on the bar member at longitudinally spaced intervals, with their axis of perforating directed generally laterally thereof. A more detailed description of a typical perforating apparatus is contained in U.S. Pat. No. 4,428,440, which is incorporated herein by reference.
The shaped charge most common in well perforating is a conical shaped charge. A conical shaped charge consists of an explosive material having a substantially conical cavity formed in the front face. A metal liner material covers the face of the cavity. Upon detonation the shape of the explosive cavity focuses and propagates a progressive wave front against the outside surface of the metal liner. At the pressures generated the metal acts as a fluid. Metal in fluid form is focused into a "jet" stream. The resultant focusing force moves particles to form a jet which lengthens as the wave front advances from apex to base of the conical cavity. The extreme high pressure, particle laden, jet stream breaks down and moves aside any material upon which it impinges. Penetration of such material is a result of the amount of pressure and the kinetic energy in the jet stream. One form of conical shaped charge used in well perforating is illustrated in U.S. Pat. No. 4,387,773, which is incorporated herein by reference.
The present invention provides method and apparatus for perforating a well casing and the surrounding formations using a lined shaped charge employing an explosive material consisting of quantities of two explosive materials having different detonation rates.